Why Classify? Classification: the division of organisms into groups, or classes, based on specific characteristics For thousands of years, humans have classified things based on usefulness Biologists use system to classify things— this system groups organisms according to their shared characteristics
Classification of living things makes it easier for biologists to answer many important questions, such as: How many known species are there? What are the defining characteristics of each species? What are the relationships between these species?
How Do Scientists Classify Organisms? Great Greek philosopher and scientist Aristotle (384-322 BCE) began classifying animals into logical groupings more than 2000 years ago
– He arranged all living things in an ascending ladder with humans at the top– Animals were separated into two major groups—those with red blood and those without red blood (very similar to our modern classification of invertebrates and vertebrates )
In 1700s, Swedish scientist Carolus Linnaeus founded modern taxonomy Taxonomy : the science of describing, naming, and classifying organisms Linnaeus tried to classify all living things based on their shape and structure
– Species were given distinctive two-word names Described a seven - level system of classification, which is still used today, although it has gone through many changes.
Classification Today Taxonomists use the 7-level system to classify living things based on shared characteristics Also use shared characteristics to hypothesize how closely related living things are The more characteristics they share, more closely related the organisms are
Example: platypus, brown bear, lion, and house cat are thought to be related because they share manycharacteristics. These animals have hair and mammary glands, so they are grouped together as mammals. They can be further classified into more-specific groups.
Branching Diagrams Each characteristic on the lines of the branch are shared by the animals to the right of it As you move up the line, the animals are more closely related to each other
Levels of Classification Every living thing is classified into one of six kingdoms:1. KINGDOM: largest, most general group2. PHYLUM: sorted from the kingdom3. CLASS: all living things in a phylum are sorted into classes4. ORDER: each class includes one or more orders5. FAMILY: one or more orders6. GENUS: families are broken into genera
Genera are sorted into species A species is a group of organisms that are closely related and can mate to produce fertile offspring Let’s see the classification of a housecat from kingdom Animalia to genus and species, Felis domesticus
Kingdom AnimaliaAll animals are in the kingdom animalia
Phylum ChordataAll animals in the phylum Chordata have a hollow nerve cord. Most have a backbone.
Class MammaliaAnimals in the class Mammalia have abackbone. They also nurse their young.
Order Carnivora Animals in the order Carnivora have abackbone and nurse their young. They also have special teeth for tearing meat.
Family Felidae Animals in the family Felidae are cats. They have a backbone, nurse their young and have special teeth fortearing meat. The Felidae have five toes on the front feet, four on the hind ones, all armed with strong "retractile claws”.
Genus Felis Animals in the genus Felis have traits ofother animals in the same family. However, these cats cannot roar; they can only purr.
Species Felis domesticus the species Felis domesticus is thecommon house cat. The house cat sharestraits with all of the organisms in the levels above the species level, but it also has unique traits.
Scientific Names A scientific name is always the same for a specific kind of organism no matter how many common names there might be Before Linnaeus, different scientists named organisms differently, so an organism could have more than one name Example on next slide…
Example:What do the mountain lion, cougar, and puma all have in common? They are ONE ANIMAL withseveral common names! The scientific name for all three common names is Felis concolor, no matter where you go in the world!
Two-Part Names Linnaeus simplified the naming of living things by giving each species a two-part scientific name For example, the scientific name for the Asian elephant is Elephas maximus. First part of name Elephas is genus name. Second part, maximus, is species name. No other species has both this genus name and species name.
All genus names begin with a capital letter All species names begin with a lowercase letter Usually, both words are Equus caballus underlined or italicized Scientific names are usually in Greek or Latin, and contain information about the organism
Dichotomous Keys Dichotomous key: an aid that is used to identify organisms and that consists of the answers to a series of statements There are only 2 alternative responses to each statement Either the chosen statement identifies the organism or the person is directed to another pair of statements
By working through the statements in the key in order, the person can eventually identify the organismDichotomous Key for Identifying Candy
A Growing System People are still discovering and classifying organisms Some newly discovered organisms fit into existing categories Sometimes, someone discovers new evidence or an organism is so different from other organisms that it doesn’t fit into a category.